Influenza A virus replication induces cell cycle arrest in G0/G1 phase.

Many viruses interact with the host cell division cycle to favor their own growth. In this study, we examined the ability of influenza A virus to manipulate cell cycle progression. Our results show that influenza A virus A/WSN/33 (H1N1) replication results in G(0)/G(1)-phase accumulation of infected cells and that this accumulation is caused by the prevention of cell cycle entry from G(0)/G(1) phase into S phase. Consistent with the G(0)/G(1)-phase accumulation, the amount of hyperphosphorylated retinoblastoma protein, a necessary active form for cell cycle progression through late G(1) into S phase, decreased after infection with A/WSN/33 (H1N1) virus. In addition, other key molecules in the regulation of the cell cycle, such as p21, cyclin E, and cyclin D1, were also changed and showed a pattern of G(0)/G(1)-phase cell cycle arrest. It is interesting that increased viral protein expression and progeny virus production in cells synchronized in the G(0)/G(1) phase were observed compared to those in either unsynchronized cells or cells synchronized in the G(2)/M phase. G(0)/G(1)-phase cell cycle arrest is likely a common strategy, since the effect was also observed in other strains, such as H3N2, H9N2, PR8 H1N1, and pandemic swine H1N1 viruses. These findings, in all, suggest that influenza A virus may provide favorable conditions for viral protein accumulation and virus production by inducing a G(0)/G(1)-phase cell cycle arrest in infected cells.

Hepatitis B virus genotype G monoinfection and its transmission by blood components.

An acute hepatitis B virus (HBV) infection was diagnosed in a regular apheresis (plasma/platelet) donor by the hepatitis B surface antigen (HBsAg) assay and minipool nucleic acid amplification technology (NAT). The acute infection was confirmed by detection of anti-HBc (IgM) and anti-HBs 2 weeks later. The donor showed no clinical symptoms and had normal alanine aminotransferase levels. He had a history of weekly apheresis plasma or platelet donations. Archived material from the donor and the respective recipients was investigated by sensitive HBV NATs as part of a look-back procedure. HBV DNA was detectable in previous donations as well as in two recipients transfused with platelet concentrates. The rare HBV genotype G was identified in all HBV-DNA-positive samples. Strong evidence of genotype G monoinfection was obtained by clonal sequencing, HBV genotype line probe assay, genotype-specific NATs, and restriction pattern analysis. In contrast to previously described genotype G infections, which all appeared as coinfections with genotype A, neither the hepatitis B e antigen (HBeAg) nor anti-HBe was detectable in any of the samples. This shows that HBeAg is dispensable for viral replication. The delay in detecting HBsAg in both the donor and recipient samples may be explained by either decreased genotype G-specific synthesis of incomplete viral forms in early HBV infection or the lower sensitivity to genotype G of the current HBsAg assays. In conclusion, this reported case of an HBV infection was caused exclusively by genotype G.